Many popular search engines run an auction to determine the placement of advertisements next to search results. Current auctions performed by search engines, such as Google™ and Yahoo!®, permit advertisers to specify a single amount as their bid in the auction. This bid can be interpreted as the maximum amount the advertiser is willing to pay per click on its advertisement. In some current systems, the advertisers pay for each user who clicks on their advertisement, and the amount charged depends on the bids of other advertisers participating in the auction.
When search queries are received at the search engines, the bids may be used to rank advertisements related to the search queries for presentation with the search results. Advertisers may seek to have a high ranking, which can correspond to a more prominent display of their advertisements.